1. Department
of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, Troy, New York 12180, United States
2. State
Key Laboratory of Luminescence and Applications, Changchun Institute
of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, China
3. State
Key Laboratory on Integrated Optoelectronics, College of Electronic
Science and Engineering, Jilin University, Changchun 130012, China
4. Spin
Engineering Physics Team, Korea Basic Science Institute (KBSI), Daejeon 305-806, Republic of Korea